German Patent Disclosure Document DE-OS 26 08 611 discloses an arrangement in which pulses are derived from a tachometer generator whose frequency is proportional to the speed to be regulated, for example the speed of a spinning turbine. The cycle duration and the timing of the gaps between the pulses is inversely proportional to speed. The pulses trigger a flip-flop which produces pulses of a constant pulse length. The length of these pulses is compared with the cyclical duration of the tachometer pulses. Motor current is disconnected if the cyclical duration or duration of a period of the tachomater pulses is less than the constant pulse length; the motor current is connected again when the cyclical duration of the tachometer pulses becomes longer than the constant or reference pulse length. The control is a two-point, ON-OFF control in which the motor speed constantly varies or hunts about the desired value. The information which is contained in the tachometer pulse train regarding actual instantaneous motor speed is utilized only incompletely. U.S. Pat. No. 3,864,610 discloses an arrangement with a control circuit which has no 0 timing circuit with constant pulse length of its output.